22 
  
  
For Swedish conditions, assuming an average strip length of Tes 4e 0 
approximately 10 stereo models and the purpose being topogra- asy year 
phic mapping at a scale 1:2 000 of a narrow band along the phic Maps 
strip from aerial photographs in the scale 1:10 000 - 1:13 000, major par 
the following principles are suggested for the location of tion for 
ground control as a basis for aerial triangulation a lot of 
portance 
a) complete geodetic control in the first and last model of 
the strip, The major 
to by-pas 
b) additional planimetric control as a traverse with average ror OS 
sidelengts x2 km, fices an 
the scale 
c) elevation control in the area to be mapped and along the prestudy 
strip for datum and longitudinal tilt, Th 
[he numbei 
d) a pair of additional elevation control points (w-control) E Lion nes : 
at intervals Æ3 km. 
Depending on conditions given by topography, vegetation, access 3.5 Map | 
to triangulation points etc, the costs for geodetic control can For theidı 
be reduced by 10 to 30%. 
a topograj 
ventional 
3.4 Determination of Feasible Routes a coordin: 
pending or 
In the preliminary design stage, feasible routes are determined At 
within the terrain corridor delimited in the route location. presen 
sed by the 
In urban or sub-urban areas the width of the terrain corridor 1 Wild A 
is often so limited by the development plan for the area that 1 Wild As 
the analysis of the corridor and the fitting of a road centre 4 Wild Af 
line can be made directly on a topographic map in the scale 20 Balpl 
1:2 000. Such maps are often available to the designer from the Bip ©) 
city planning offices. The autogr 
In rural areas the terrain corridor can be rather wide, resul- ! * three qii 
ting in high map costs for the whole area. In such areas it is errors Gt 
advantageous to start the analysis directly in the stereo model 25 = da 
which generally contains more complete information than a map. , A 
This technique has been used in Sweden for more than fifteen For e Cn 
years. The photogrammetric equipment consists of a Balplex Plot- a S 
ter with four projectors and a hydraulic lift. Since the plotter ar 
has optical projection it is possible to do the topographic plan- 
ning directly in the stereo model. Geological information can be 
received from the aerial photographs with the aid of a mirror 3160 Photo 
stereoscope. The horizontal alignment of the proposed road centre " 
lines is presented on a planimetric map in the scale of the ste- In areas 
reo model, usually 1:4 000. Corresponding longitudinal profiles iC]  Cond 
and necessary cross-sections are also measured. dari 
aries and 
proved to 
The choice between the proposed centre lines is made on the basis 
of an analysis of the consequences and costs of each alternative 
with respect to construction, vehicle operation, maintenance etc. E 
alternativ 
pretations 
Thus the area where a detailed topographic map is needed has been fer Plann] 
reduced to a narrow band around the selected centre line. 15C0V 
During the 
tantly inc